Show AddEnvironmentVariables() in the sample code

Author: nblumhardt

samples/SimpleWebSample/Program.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.IO;
 using Microsoft.AspNetCore;
 using Microsoft.AspNetCore.Hosting;
@@ -13,6 +13,7 @@ public class Program
             .SetBasePath(Directory.GetCurrentDirectory())
             .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
             .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
+            .AddEnvironmentVariables()
             .Build();
 
         public static int Main(string[] args)